For several applications in for example the technical fields of driver analysis in vehicles and user control of personal computers there is a need to acquire information on the users' eye gaze direction, the movements of the eyes and the eyelids and the position of the user. Among possible methods to image and analyze the users eyes there is a group of methods based on detecting reflections on the cornea. Knowledge of the interrelationship between the imaging system and the light source that is reflected in the pupil enables calculation of the eye gaze direction. Using only one camera, it is sometime difficult to correctly determine the eye gaze. This may be solved by using two or more light sources, movable light sources or more than one camera. Using two cameras, a more accurate position and direction of the object's eyes may be calculated, compared to a single camera device.
When the light source is close to the optical axis of the imaging system there will be an internal reflection in the eye which appears brighter than the surrounding, this is called bright eye effect. If the light source is sufficiently removed from the optical axis, the light source will illuminate the eye and the surrounding area without causing an internal reflection, referred to as dark eye effect. A pupil in bright-eye condition may be easier to detect in contrast to its surroundings, but there may be advantages to determine the reflections from the light source on a pupil in dark-eye effect conditions.
In order to acquire a satisfactory dark-pupil image, the light source (flash) should be separated from the camera in the order of 10 degrees from the perspective of the user. In a case where two cameras are used (stereo imaging) the two cameras should also be separated by about 7-10 degrees. For example, in a use case where a person is sitting some 60 centimeters from the eye tracker, the complete imaging device will have two cameras and two light sources arranged over a width of roughly 30 cm. Such a device becomes relatively bulky, and is difficult to implement in a space restricted environment, such as an automobile.
Current eye gaze tracking systems are often adapted for research and development or prototype use. It is therefore desired to develop a device which may be more suitable for mass market use in for example automotive applications or personal computers. Simultaneously it is important that a high functional detection rate and accuracy is maintained so that user acceptance is not lost.